Process and installation for forming a layer on a substrate

ABSTRACT

A method and installation for forming a coating on a substrate, wherein the substrate is contacted with a gas treatment atmosphere in order to carry out said coating. The gas treatment atmosphere includes a primary gas treatment mixture comprising excited or unstable gaseous species obtained from a device which converts an initial gas mixture into said species, and an adjacent gas treatment mixture comprising at least one gas precursor required to form said coating, whereby the adjacent mixture is not transported via said device. The adjacent gas treatment mixture is injected into the flow of the primary gas mixture when the gas exits from the device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to the field of surface treatments of substrates,whether these are metallic or non-metallic, such as, polymer, textile,paper, glass, or even wood, plaster or tile substrates, and whetherthese substrates are flat or are in the form of a volume, thesesubstrates being used in extremely varied fields including metallurgy,bottle-making, flat glass, plastic packaging, etc.

2. Description of the Related Art

It is known that these surface treatments are usually carried out forthe purpose of improving the adherability and wettability of thesesubstrates, or else for introducing a friction coefficient, corrosionresistance, color, an optical index, etc.

Among the very numerous methods available in the literature for carryingout these surface treatments are liquid-phase treatments, low-pressureplasma treatments, corona-discharge treatments or flame brushing.

The Applicant has recently proposed, in documents EP-A-734 461 andEP-A-734 462, a process for depositing silicon-based layers on asubstrate, in which process the substrate is placed in the remote-plasmaposition of an apparatus for forming excited or unstable gaseous speciesso as to be brought into contact with a gaseous treatment atmospherenecessary for producing the coating, obtained from the following twocomponents:

a primary gas treatment mixture, as obtained at the gas outlet of theapparatus, which comprises excited or unstable gaseous species resultingfrom the transformation in the apparatus of an initial gas mixture; and

an adjacent gas treatment mixture which comprises a gaseous siliconprecursor and which has not passed through the apparatus in question.

These European documents, together with document FR-A-2 692 730 also inthe name of the Applicant, disclose a device for forming excited orunstable gaseous species, operating approximately at atmosphericpressure, and suitable for implementing the process described in theabovementioned European documents.

Although these processes undoubtedly constitute an advance over theexisting techniques (liquid phase, flame brushing, low-pressure plasma,etc.), the Applicant has shown by its studies that there may be furtherimproved, especially so as to increase the transformation efficiency ofthe reactive gas (for example silane) and to reduce the production ofundesirable particles (powders).

Specifically, an insufficient transformation efficiency of the reactivegases correspondingly limits the rate of growth of the layer depositedand therefore the productivity and economic benefit of the process.

SUMMARY OF THE INVENTION

It is one of the objectives of the present invention to provide asolution to the abovementioned technical problems.

To do this, the invention relates to a process for forming a coating ona substrate, in which the following steps are carried out:

at least one apparatus for forming excited or unstable gaseous speciesis used, in which an initial gas treatment mixture is transformed so asto obtain, at the gas outlet of the apparatus, a primary gas treatmentmixture which comprises excited or unstable gaseous species and which issubstantially free of electrically charged species;

the substrate is brought into contact, at a pressure close toatmospheric pressure, with a gaseous treatment atmosphere in order todeposit the coating, this atmosphere being obtained from the primary gasmixture and an adjacent gas treatment mixture which comprises at leastone gaseous precursor needed to form the desired coating, and which hasnot passed through the said apparatus;

the process being characterized in that the adjacent gas mixture isinjected into the stream of primary gas mixture as obtained at the gasoutlet of the apparatus.

The process according to the invention may moreover have one or more ofthe following technical characteristics:

the injection of the adjacent gas mixture into the stream of primary gasmixture is made in the following manner:

i) means are used for separating the stream of primary gas treatmentmixture, as obtained at the gas outlet of the apparatus, into at leasttwo separate streams;

j) the injection of adjacent gas mixture is made to enter between saidat least two separate streams of primary mixture;

the residual oxygen content of the gaseous treatment atmosphere is lessthan 500 ppm and preferably between 5 and 100 ppm;

the dew point of the gaseous treatment atmosphere is less than −20° C.and preferably less than −30° C.;

throughout or during part of the time the substrate is in contact withthe gaseous treatment atmosphere, the substrate is at a temperature ofbetween 50 and 350° C., and more preferably between 100 and 300° C.(whether the substrate undergoes heating during the contact or else, forexample, whether it reaches the contact zone already hot);

the treated substrate is brought opposite the gas outlet of saidapparatus, where appropriate opposite the gas outlets of severalapparatuses placed in parallel over the width of the substrate and/orsuccessively opposite the gas outlets of several apparatuses placed inseries, by a conveying system passing through an internal space boundedby a shrouding assembly isolated from the surrounding atmosphere, theassembly being connected in a sealed manner to the apparatus orincluding the apparatus;

the nature of the coating produced on the substrates belongs to one ofthe following categories: a metal oxide or a metal oxynitride;

the coating produced is a coating comprising silicon and the adjacentgas treatment mixture therefore includes at least one gaseous siliconprecursor;

at least one of said apparatuses, in which the initial gas treatmentmixture is transformed, is the site of an electrical discharge createdbetween a first electrode and a second electrode which extend in anelongated main direction, the initial gas mixture passing through thedischarge transversely to the electrodes and to this main direction; and

a layer of a dielectric material is placed on the surface of at leastone of the electrodes, opposite the other electrode.

The invention also relates to an installation for forming a coating on asubstrate, suitable especially for implementing the process describedabove, and comprising:

at least one apparatus for forming excited or unstable gaseous species,which is capable of transforming an initial gas treatment mixture so asto obtain, at the gas outlet of the apparatus, a primary gas treatmentmixture which comprises excited or unstable gaseous species and which issubstantially free of electrically charged species;

means for feeding an adjacent gas treatment mixture, comprising at leastone gaseous precursor needed to form the coating, which does not passthrough the apparatus, and is capable of forming, with the primary gastreatment mixture as obtained at the gas outlet of the apparatus, agaseous treatment atmosphere to be brought into contact, at a pressureclose to atmospheric pressure, with the substrate in order to producethe coating;

the installation being characterized in that said means for feeding theadjacent gas mixture allow it to be injected into the stream of primarygas mixture as obtained at the gas outlet of the apparatus.

According to one of the embodiments of the installation according to theinvention, the means for feeding the adjacent gas mixture into thestream of primary gas mixture comprise:

i) means for separating the stream of primary gas mixture as obtained atthe gas outlet of the apparatus into at least two separate gas streams;

j) means for injecting the adjacent gas mixture between said at leasttwo separate streams of primary gas mixture.

BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS

Further features and advantages will become apparent from the followingdescription, given solely by way of illustration and with reference tothe appended drawings in which:

FIGS. 1A and 1B are schematic representations of an installation forforming a coating on a substrate according to the prior art;

FIG. 2 is a schematic representation of one embodiment according to theprior art, such as one comprising a tunnel;

FIG. 3 is a partial schematic representation of an installationaccording to the invention;

FIG. 4 is a partial detailed view of the means present in FIG. 3 forseparating the stream of primary gas mixture output by the apparatusinto two separate streams and for injecting the adjacent gas mixturebetween these separate streams of primary gas mixture.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1A and 1B therefore provide partial schematic representations of acoating installation according to the abovementioned prior art (Europeandocuments).

Shown schematically in FIG. 1 by the reference 4 is an apparatus forforming excited or unstable gaseous species, supplied at its gas inlet 5with an initial gas treatment mixture 7. A primary gas treatment mixture8 is then obtained at the gas outlet 6 of the apparatus.

Moreover, a substrate 1, placed opposite this gas outlet 6, is exposedto an adjacent gas treatment mixture which is fed, in the embodimentsshown, via one or two gas inlets (10 in the case of FIG. 1A and 9 and 10in the case of FIG. 1B), this adjacent treatment mixture not passingthrough the apparatus 4 for forming excited or unstable gaseous species.

Shown symbolically in these figures by the dashed rectangle 30 is thezone in which the primary and adjacent gas treatment mixtures interactso as to produce the required coating on the substrate 1.

FIG. 2 shows one particular embodiment of a coating installationaccording to the prior art already mentioned, such as comprising atunnel 3 defining an internal space 31 through which the substrate 1 isconveyed with the aid of a conveying means 2 (for example a conveyorbelt).

The substrate is then brought opposite the gas outlet 6 of the apparatus4 mentioned above within the context of FIGS. 1A and 1B, where it comesinto contact with the primary gas treatment mixture 8 and with theadjacent treatment mixture being fed via the two gas inlets 9 and 10.

It will be noted that the embodiment shown in FIG. 2 allows thesubstrate 1 to be treated by several apparatuses for forming excited orunstable gaseous species placed in series, the apparatuses placed at 11and 12 not having been shown in order not to unnecessarily clutter upthe figure, while the reference numbers 13 and 29 for their partillustrate additional examples of inlets of adjacent treatment mixturesthat have not passed through the apparatuses.

FIG. 3 shows a schematic and partial representation of a device forforming a coating on a substrate suitable for implementing the processaccording to the present invention.

This FIG. 3 shows an apparatus 4 for forming excited or unstable speciesprovided with its gas inlet 5, capable of admitting the initial gasmixture 7 that has to be transformed in the apparatus, and with a gasoutlet 6 capable of producing the primary gas treatment mixture whichincludes the excited or unstable gaseous species.

As will be more clearly seen below in the context of FIG. 4, theinstallation is also equipped with means capable of separating thestream of primary gas mixture from the gas outlet of the apparatus intotwo separate streams, the means comprising here a cylindrical component40 provided with a slot 42 over all or part of the length of thecomponent 40.

As may be very clearly seen in FIGS. 3 and 4, the stream of primary gasmixture from the gas outlet 6 of the apparatus is therefore in factdivided into two separate streams 8 a and 8 b, whereas an adjacent gastreatment mixture, which includes at least one of the gaseous precursorsneeded to produce the coating on the component 1, for example a gaseoussilicon precursor, again for example, an organometallic compound,escapes from the slot 42 of the component 40.

Such a configuration therefore makes it possible for this adjacent gasmixture to be injected into the stream of primary gas mixture asobtained at the gas outlet of the apparatus 4.

As will be clearly apparent to those skilled in the art, although theembodiment shown in FIG. 4 illustrates an injection of the adjacentmixture using a slot, many other methods of injection may be envisagedwithout departing from the scope of the present invention, such as aporous medium, a pipe with orifices (holes), multiple slot systems, etc.

It has therefore been possible to compare the effectiveness of thedevices according to FIG. 1A, FIG. 1B and FIG. 3 in order to producesilicon-based coatings on specimens consisting of polished glass plates,approximately 50 mm in size, the specimen holder moving at a rate ofabout 10 cm/minute beneath the discharge.

For safety reasons and for ease of implementation, the adjacent gasmixture used was obtained from a bottle containing a N₂/1.9% SiH₄mixture.

The comparative results obtained may be summarized in the following way:

a) first test series: using the device of FIG. 1A (unsymmetrical lateralinjection of the adjacent mixture).

The adjacent mixture was injected through a lateral slot about 10 mm inwidth, located about 30 mm from the primary gas mixture jet 8 comingfrom the discharge.

The adjacent mixture flow rate used was about 12 liters/hour.

By means of this injection, it was therefore possible to demonstratethat silicon oxide layers could be deposited at a mean rate of about 1Å/s, the amount of silane used with respect to the rate of depositionthen being about 3.3×10⁻³ liters of SiH₄ per Å.

Moreover, it was found that such an arrangement generates a notinsignificant amount of silica powder, which signifies that a notinsignificant part of the silane flow does not reach the region of theprimary gas mixture jet because of the remoteness of the adjacentmixture injection.

b) for a second test series using the device in FIG. 1B (symmetricallateral injections of adjacent mixture), we have therefore injected theadjacent gas mixture on each side of the discharge, at approximately 5mm from the central jet of primary gas mixture.

The adjacent injections were made through slots approximately 0.5 mm inthickness, ensuring an ejection rate close to 3 m/s; the adjacent gasflow rate was close to 1 liter/h.

Such operating conditions have made it possible to deposit silicon oxidelayers at a mean rate of about 1.2 Å/s, therefore corresponding to anamount of silane used with respect to the rate of deposition of2.31×10⁻⁴ liters of SiH₄ per Å.

It may therefore be seen without any difficulty that the efficiency ofsilane transformation, obtained by means of such a symmetricalinjection, closer to the jet of primary gas mixture obtained in remoteplasma mode, is approximately 15 times greater than that obtainedpreviously within the context of the configuration of FIG. 1A;

c) third test series using the device of FIG. 3 (injection into thestream of primary mixture).

As clearly shown schematically in this FIG. 3, this third test seriesused a separation of the jet of primary gas mixture output by thedischarge head into two, and the injection of the adjacent gas mixturecomprising the gaseous silicon precursor between the two separate jets 8a and 8 b.

Such a configuration therefore clearly makes it possible to trap thestream of adjacent mixture in the volume bounded by the two jets ofprimary gas mixture in order to facilitate the mixing and the reactionof the adjacent gas on the surface of the substrate.

In this configuration, the slot 42 for injecting the adjacent gas wasdecreased to about 0.25 mm in order to allow the rate of output of thereactive gas to be increased to approximately 5 to 6 m/s.

The two spaces for outputting the primary gas treatment mixture aroundthe component 40 had a width of about 0.5 mm, making it possible toretain velocities close to 10 m/s for the two corresponding gas jets.The flow rate of adjacent gas was then close to 0.2 liters/h.

Such a configuration therefore made it possible to deposit silicon oxidelayers at a rate close to 2.5 Å/s, corresponding to an amount of silaneconsumed with respect to the rate of deposition close this time to2.2×10⁻⁵ liters of SiH₄ per Å.

It may therefore be very clearly concluded that the silanetransformation efficiency for such a central configuration of theadjacent gas mixture within the remote plasma is approximately 150 timesgreater than that obtained within the context of the first configurationaccording to FIG. 1A and approximately 10 times greater than the resultsobtained within the context of the configuration according to FIG. 1B.

It is therefore apparent how much such a configuration correspondinglyimproves the economic but also the qualitative aspects of the process,the amount of silica powder produced by such a configuration beingmarkedly less than that produced by the previous configurations.

What is claimed is:
 1. Process for forming a coating on a substrate,comprising the following steps: converting an initial gas mixture in atleast one apparatus for forming excited or unstable gaseous species toobtain, at a gas outlet of the apparatus, a primary gas treatmentmixture which comprises excited or unstable gaseous species and which issubstantially free of electrically charged species; contacting thesubstrate at a pressure close to atmospheric pressure, with a gaseoustreatment atmosphere to deposit the coating, the gaseous treatmentatmosphere comprising said primary gas treatment mixture and an adjacentgas treatment mixture which comprises at least one gaseous precursorneeded to form the desired coating, and which has not passed throughsaid apparatus; wherein the adjacent gas treatment mixture is injectedwithin the stream of primary gas mixture obtained at the gas outlet ofthe apparatus.
 2. Process according to claim 1, wherein injection of theadjacent gas mixture into the stream of primary gas mixture comprises:separating the stream of primary gas mixture obtained at the gas outletof the apparatus into at least two separate streams; and injecting theadjacent gas mixture between said at least two separate streams of theprimary gas mixture.
 3. Process according to claim 2, wherein theresidual oxygen content in the gaseous treatment atmosphere is less than500 ppm.
 4. Process according to claim 3, wherein the residual oxygencontent in the gaseous treatment atmosphere is between 5 and, 100 ppm.5. Process according to claim 2, wherein the dew point of the gaseoustreatment atmosphere is less than −20° C.
 6. Process according to claim5, wherein the dew point of the gaseous treatment atmosphere is lessthan −30° C.
 7. Process according to claim 2, wherein during at leastpart of the time the substrate is in contact with the gaseous treatmentatmosphere, the substrate is at a temperature of between 50 and 350° C.8. Process according to claim 7, wherein the coating produced comprisesa metal oxide or a metal oxynitride.
 9. Process according to claim 8,wherein the coating produced is a film containing silicon and theadjacent gas treatment mixture includes at least one gaseous siliconprecursor.
 10. Process according to claim 2, wherein said at least oneapparatus in which the initial gas treatment mixture is transformed, isthe site of an electrical discharge created between a first electrodeand a second electrode which extend in an elongated main direction, theinitial gas mixture passing through the discharge transversely to theelectrodes and to the main direction.
 11. Process according to claim 10,wherein a layer of a dielectric is placed on the surface of at least oneof the electrodes, opposite the other electrode.
 12. Process accordingto claim 1, wherein residual oxygen content in the gaseous treatmentatmosphere is less than 500 ppm.
 13. Process according to claim 12,wherein the residual oxygen content in the gaseous treatment atmosphereis between 5 and 100 ppm.
 14. Process according to claim 1, wherein thedew point of the gaseous treatment atmosphere is less than −20° C. 15.Process according to claim 14, wherein the dew point of the gaseoustreatment atmosphere is less than −30° C.
 16. Process according to claim1, wherein during at least part of the time the substrate is in contactwith the gaseous treatment atmosphere, the substrate is at a temperatureof between 50 and 350° C.
 17. Process according to claim 1, wherein thecoating produced comprises a metal oxide or a metal oxynitride. 18.Process according to claim 17, wherein the coating produced is a filmcontaining silicon and the adjacent gas treatment mixture includes atleast one gaseous silicon precursor.
 19. Process according to claim 1,wherein said at least one apparatus in which the initial gas treatmentmixture is transformed, is the site of an electrical discharge createdbetween a first electrode and a second electrode which extend in anelongated main direction, the initial gas mixture passing through thedischarge transversely to the electrodes and to the main direction. 20.Process according to claim 19, wherein a layer of a dielectric is placedon the surface of at least one of the electrodes, opposite the otherelectrode.
 21. Installation for forming a coating on a substrate,comprising: at least one apparatus having means for converting aninitial gas treatment mixture into a primary gas treatment mixture whichcomprises excited or unstable gaseous species and which is substantiallyfree of electrically charged species, and a gas outlet means todischarge said primary gas treatment mixture; means for feeding anadjacent gas treatment mixture, comprising at least one gaseousprecursor needed to form the coating, which adjacent gas mixture doesnot pass through said at least one apparatus, to form with the primarygas mixture obtained at the gas outlet means of the apparatus, a gaseoustreatment atmosphere which is brought into contact, at a pressure closeto atmospheric pressure, with the substrate to produce the coating; andmeans for directing said feed of adjacent gas mixture within the streamof primary gas mixture obtained at the gas outlet means of theapparatus.
 22. Installation according to claim 21, wherein said meansfor directing the adjacent gas mixture into the stream of primary gasmixture comprise: i) means for separating the stream of primary gasmixture obtained at the gas outlet means of the apparatus into at leasttwo separate gas streams; j) means for injecting the adjacent gasmixture between said at least two separate streams of primary gasmixture.
 23. Installation according to claim 22, wherein said at leastone apparatus having means for converting an initial gas treatmentmixture, includes means for creating an electrical discharge between afirst electrode and a second electrode which extend in an elongated maindirection, the initial gas mixture passing through the dischargetransversely to the electrodes and to the main direction. 24.Installation according to claim 23, wherein a layer of a dielectric isplaced on the surface of at least one of the electrodes, opposite theother electrode.
 25. Installation according to claim 21, wherein said atleast one apparatus having means for converting an initial gas treatmentmixture, includes means for creating an electrical discharge between afirst electrode and a second electrode which extend in an elongated maindirection, the initial gas mixture passing through the dischargetransversely to the electrodes and to the main direction. 26.Installation according to claim 25, wherein a layer of a dielectric isplaced on the surface of at least one of the electrodes, opposite theother electrode.